Abstract: AIM To discuss the correlation between serum gamma glutamine transferase (GGT) and slow/no reflow after percutaneous coronary intervention (PCI) in elderly diabetics patients with acute coronary syndrome (ACS) and its influence on major adverse cardiovascular events (MACE). METHODS One hundred and eighty-eight elderly diabetics patients who were diagnosed as having ACS and were treated with PCI were recruited into our study. The patients were divided into two groups based on the Thombolysis in Myocardial Infarction (TIMI) flow classification and corrected TIMI frame count (cTFC): normal coronary flow (NCF) group (n=156) and slow/no reflow group (n=32). The serum level of GGT and other risk factors were measured and MACEs were recorded. RESULTS The serum level of GGT was significantly increased in slow/no reflow group compared with that in NCF group ［(49±18) U/L vs.(31±13) U/L, P<0.01］. The results of correlation analysis showed a positive correlation between GGT level and slow/no reflow (r=0.389, P<0.01). The serum level of GGT on admission was independently associated with slow/no reflow following primary PCI, in-hospital and twelve-month MACEs in elderly diabetics patients with ACS (OR=1.093, 95 CI:1.058-1.129, P<0.01; OR=1.047, 95%CI: 1.012-1.082, P<0.05 and OR=1.058, 95%CI: 1.028-1.089, P<0.01, respectively). CONCLUSION The serum level of GGT is positively associated with slow/no reflow in elderly diabetics patients with ACS and it can be used as a predictor of coronary risk.